[CMake] CMake way to achieve march=native

[Chris Stankevitz]

Hi,

What is the CMake way to get march=native?  By "CMake way" I'm looking
for something that is somewhat robust, works, doesnt' confuse CMake
itself... perhaps even works if/when anyone is going to cross compile,
etc.

The cross-compile part isn't a requirement... I'm just trying to get
you to understand what I'm after is not just to slop together a
command that happens to work today.  But if the only way is to slop
something together then that's okay too.

Thank you,

Chris